Here's some websites which contain lyrics of freedom songs. These websites also contain commentary about the role of songs in the civil rights movement or commentary about the songs themselves:

http://www.historynow.org/06_2006/interactive.html
Songs Of The Civil Rights Movement

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http://folkmusic.about.com/od/toptens/tp/CivilRightsSong.htm
Top 10 Civil Rights Songs

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http://www.cocojams.com/freedom_songs.htm
Civil Rights Songs